This invention relates to a bottle cap having internal threads and adapted to seal the neck of the bottle or jar. The invention is particularly adapted to closing bottles containing gasified liquids.
There are known screw-type bottle caps, usually made of metal, such as aluminum, in which the internal screw thread is formed on the bottle cap by the neck of the bottle at the moment at which the cap is applied, by rotating the cap, which is driven about the neck of the bottle by means of a grooved swaging roller. In these caps sealing is assured by a seal of plastic material, or some other sealing material serving the same purpose, attached to or poured into the top of the cap.
This type of cap has many disadvantages, principally because of the substantial tolerances in diameter which occur in practice with respect to the necks of the bottles to be closed, especially glass bottles. Because of these substantial tolerances, the use of this type of capsule frequently leads to defects in the threads of the necks which result in leaks and, in certain cases, make it practically impossible to unscrew the cap. Moreover, the threads formed in the cap during the closing operation appear on its outside and leave little space for external serrations, so that the user frequently encounters difficulty in unscrewing this type of cap.
Caps are also known which have internal screw threads made entirely from molded plastic material. Some of these caps have an internal sealing skirt adapted to cooperate with the internal wall of the neck of the bottle or jar to be closed. These skirts, which often have a cylindrical shape, do not insure a sufficiently tight seal because of the differences in diameter which occur in the necks of bottles such as those presently being manufactured. Up to the present no one has succeeded in making a cap of this type which insures an adequate seal over a large range of tolerances in the diameter of the necks of the bottles.
Caps are also known which are made entirely of plastic molded material in which the sealing skirt is replaced by a diaphragm in the form of a bowl which covers the upper part of the neck of the bottle. The pressure at the top of this type of screw type which is all that makes it possible to obtain a suitable seal, leads, by reason of the lack of rigidity of the bowl, to considerable difficulties in unscrewing the cap. These difficulties are particularly critical in the case in which the bottle is designed to contain a gasified liquid, since the gas has a compressive effect on the bowl which increases the grip.
It is the object of the present invention to provide a bottle cap having internal threads made entirely of a plastic material molded in one piece and comprising a group of sealing means adapted to insure perfect sealing over a very large range of tolerances of the bottle neck diameter, all while permitting the cap to be easily unscrewed by the user.
It is a further object of the invention to permit a substantial increase in the speed of molding such a screw cap by substantially facilitating the unscrewing of the internal part of the mold after the operation of molding the plastic material.
The screw-type cap according to the invention is made entirely from a single piece of molded plastic material. It comprises an internal sealing skirt adapted to be force-fitted into the neck of a bottle or jar. According to the invention the internal sealing skirt has an upper part which is substantially cylindrical after it has been screwed into the neck and an external diameter which is greater than the maximum internal diameter of the neck, after allowing for the range of manufacturing tolerances in the bottles or jars to be capped.
In accordance with the invention the substantially cylindrical upper part of the sealing skirt is extended downwardly by an inwardly directed conical portion and a substantially radial collar. The dimensions of the conical portion and the collar are such that the two parts of the sealing skirt are capable, during screwing of the cap on the neck of the bottle or jar, of so deforming that the end of the collar is deformed upwardly into contact with the wall, without interfering with the upper cylindrical portion thereof which remains in sealing contact with the internal wall of the neck.
Such an arrangement is particularly advantageous in that the said end of the collar provides, after screwing down of the cap, a by no means negligible sealing effect with respect to the liquid in the bottle to be capped, but this sealing effect ceases to exist relative to gases inside the bottle after unscrewing, once the short cylindrical upper part of the sealing skirt is completely clear of the neck of said bottle.
The gas found in this bottle may then escape outwardly, before the cap is totally free of the threads on the outside of the neck, which prevents the capsule from being violently projected upwardly after complete unscrewing, as is the case when the cap has a substantially cylindrical sealing skirt with a height substantially greater than the maximum change in the axial position of the cap which may be engendered by its screwing or unscrewing.
It is equally important, in the embodiment of the cap according to the invention, that said end of the collar cannot be subjected after screwing down, to an excessive pressure toward the upper part of the bottle, which would be capable of creating a lasting seal at the level of this end of the collar, comparable to the above-mentioned use of a cylindrical sealing skirt having an excessive height and capable of causing the same abrupt projection effects on the capsule after unscrewing.
According to the invention, in order to insure perfect sealing, the cap also comprises, in combination with the sealing skirt, a first substantially axial lip positioned in the bottom of the cap and inclined slightly inwardly so as to cooperate, during screwing down of the cap, with the upper edge of the bottle, by applying itself thereto while deforming inwardly, and a second substantially radially lip projecting inwardly of the cap so that during the unscrewing of the latter, the second lip may be applied, while deforming inwardly, against the external wall of the neck.
In a preferred embodiment of the cap according to the invention the top thereof is thin and curved inwardly of the jar so as to be capable of deforming toward the outside during the screwing down of the cap on the neck.
The wall of the cap according to the invention advantageously comprises, beneath the internal threads, a smooth cylindrical portion extending toward the bottom as an outwardly tapered conical portion. The conical portion makes it possible to facilitate the introduction of the cap onto the neck at the moment of screwing while the smooth cylindrical portion makes it possible to correctly guide the cap during this operation, which may then be carried out automatically and at high speeds.
As is well known, the molding of this type of screw cap from plastic material necessitates the use of a mold having two parts between which the plastic material is injected. Because of the internal thread, it is necessary, in order to extract the cap after the molding operation, to proceed by unscrewing the cap from the inner part of the mold. During this unscrewing operation it is desirable to hold the cap in a fixed position with respect to a member of the mold. To obtain this result blocking means are generally provided which may consist of projections from the capsule cooperating with recesses in the mold, or vice-versa. These means are generally placed on the periphery of the external wall of the cap. In view of the relatively thin nature of this wall, these blocking means may consist of a single circular row of projections or perforations.
The present invention makes it possible to improve the blocking of the capsule with respect to the mold during the unscrewing operation and thus carry out this operation in an automatic manner at very high speed.
In accordance with the invention, blocking means are positioned on the internal wall of the bottom of the cap inside the sealing skirt. This internal arrangement makes it possible to provide several circular rows of blocking projections or analogous recesses.
The mold adapted to the manufacture of a cap according to the invention has an inner part comprising a stationary central core surrounded by a socket capable of rotating about said core and of being axially displaced with respect thereto in order to permit the extraction of the molded cap held in position by the blocking means fixed to the central core.
Moreover, in order to improve the sealing, the cap in question is preferably provided with internal threads projecting from its external skirt which do not stop abruptly at their lower end, with a profile similar to a quarter of a sphere connecting it to the internal surface of said external skirt having a maximum diameter and corresponding to the bottom of said threads. Instead, the section of lower part of said threads decreases much more slowly toward their lower end in a manner comparable to that of the section of the hollow threads formed in the lower part of the neck of the bottle to be capped.
It will be understood that, taking into account the plasticity of the material constituting said caps and the possibilities of local compression of this material, it is possible to obtain in this manner a very much improved seal which could not be obtained by means of threads having a constant section, in which case it is necessary to leave a sufficient play to permit sliding without excessive friction of the external surface of said internal threads inside the hollow threads formed on the external part of the necks of the bottles.
It will be noted that the sealing contact of the lower ends of the threads against the wall of the hollow threads of the necks of the bottles considerably improves the seal because the liquid which may pass between the cap and the neck of the bottle at the level of the parts having a constant section of said helical threads, is stopped above the lower end of these threads having a slowly decreasing section.
In most cases, this reduction in the section of the threads produced by grooving the neck of the bottle takes place by imparting a horizontal direction to the lower edge of this groove, so that it makes, with the lower edge of the same thread, an angle corresponding to the pitch of these helical threads.
In this case it follows that, in like manner, the lower edge of the end of the lowermost turn of the threads which are in relief and provided on the inside of said cap of plastic material also has a horizontal direction.